1. Field of the Invention
The present invention relates to liquid filters and relates more particularly to a high efficiency liquid filter which prohibits fibrous or other debris from matting or entangling itself on the straining media of the filter elements and eliminates the problems encountered in conventional automatic washing and backwashing filters.
2. Description of the Prior Art
Various types of liquid filters have been using for removing fibrous or other debris from a liquid or water passing therethrough. During filtration process, fibrous or other debris may mat or entangle itself on the surface of the filter elements to block up the straining media thereof or, bigger fibrous or debris may penetrate through the straining media of the filter elements, causing incomplete filtration problem. For example: bacteria, particles size between 0.2 to 20 micron may still be found in filtrate obtained through conventional submicron filters (0.2-0.1 micron), ultrafilters (0.1-0.001 micron) or reverse osmosis filters (0.01-0.0001 micron). In U.S. Department of Health Education and Welfare; Public Health Service from Health Laboratory Science Vol. 12, No. 4 October 1975, there was a report regarding "Gram-Negative bacteria in hemodialysis systems" page 328 paragraph 4 indicating that "the most effective means of treating water for dialysis present in use appears to be reverse osmosis (RO); low numbers of Gram-Negative bacteria will, however, penetrate this barriers and, in time, colonize the downstream portion of the R.O. unit as in the case with absolute filters".
Regular liquid filter manufacturers have been continuously developing liquid filters for removing fibrous or other debris from liquid. To eliminate fibrous or other debris from matting or entangling itself on the straining media, some manufacturers provide diatomaceous filters for service while some others adopt backwashing method or use wire brushes. Some of these examples are outlined hereinafter.
1. Backwashing liquids may be supplied from an external source and at a pressure above the pressure of the fluid in the strainer, exemplary of this is U.S. Pat. No. 3,074,560;
2. A plurality of wire brushes may be employed which engage the filter plate and remove the sediment therefrom, exemplary of this is U.S. Pat. No. 3,017,029;
3. With the filter medium of a scouring device arranged to operate upon the filter surface to cleans the same of matter deposited thereon, in the process of filtration; also in means for flushing the filter to remove the impurities removed from the filter medium, exemplary of this is U.S. Pat. No. 422,122 dated Feb. 25, 1890;
4. An automatic backwashing strainer having a fixed straining medium on a rotation, backwashing device, the backwashing device of the rotary type provide high pressure liquid such as hot water for backwashing, exemplary of this is U.S. Pat. No. 4,315,820;
5. Filters of the type where in a bed or coat of filter-aid material, such as diatomaceous earth, is deposited on same kind of permeable support or element, exemplary of this is U.S. Pat. No. 2,826,308; and
6. Smooth surface filters, exemplary of this is U.S. Pat. No. 1,007,449.
The above-mentioned various different designs provide more or less better filtration effect in removing fibrous or other debris from liquids. However, these filters can not eliminate fibrous or other debris from matting or entangling itself on the straining media. While penetrating through the straining media under high fluid pressure, fibrous or other debris in the liquid tend to mat and entangle itself on the straining media, causing blocking problem. Using rotary wire brushes or blades to remove fibrous or other debris from the straining media may simultaneously squeeze some of which to enter the open spaces in the straining media, causing matting problem. Therefore, fibrous or other debris can not be completely removed from the straining media through conventional backwashing filters or by using conventional rotary wire brushes. When the open spaces in the straining media are partly blocked up with fibrous or other debris, liquid pressure will be simultaneously increased to force the open spaces in the straining media to expand and therefore, metamorphoses, bacteria, gelatins or emulsions in size bigger than the open spaces in the barriers may be carried by the liquid to penetrate therethrough and contaminate the filtered liquid.